The town was an ancient Moabite settlement, and is mentioned in the Bible.
"Aroer, which is on the edge of the valley of Arnon" (Deut. ii. 36), is probably represented by the present ruins of 'Arzā'ir on the north bank of the Arnon ravine, about eleven miles (18 kilometres) from the mouth of the river (Tristram, "Moab," pp. 129-131). The city was still standing in the time of Eusebius. This place was usually described by its situation, in order to distinguish it from other localities of the same name (Deut. iii. 12, iv. 48; Josh. xii. 2, xiii. 9; Judges xi. 26; II Sam. xxiv. 5).
It appears first as having been captured by the Amorite king Sihon from Moab (compare Num. xxi. 26). It should be noted that in the Mesha inscription, l. 26, it is mentioned as having been built by the Moabites. After Israel's attack on the Amorites, it was assigned as part of the territory of the tribe of Reuben, whose southern frontier it marked. This is the city mentioned in Num. xxxii. 34, with the southern towns, as having been built by the children of Gad before the distribution of the land. When Hazael and his Syrians took from Israel the territory across the Jordan, Aroer is given as its southern limit (II Kings x. 33). It is clear, from Jer. xlviii. 19, that the Moabites ultimately recovered it from the Israelites.